Hepatitis C(HCV) is the major cause of parenterally transmitted non-A, non-B hepatitis (Choo et al., 1989 Science 244:359-362; Kuo et al., 1989, Science 244:362-364) with a prevalence of 1-3% throughout the world (Davis et al., 1998, Hepatology 28(Suppl 4, pt 2):99A). Chronic disease develops in 60-85% of patients, with cirrhosis representing a major hallmark of HCV infection. Among patients whose infection progresses to cirrhosis, as many as 1-4% develop hepatocellular carcinomas annually (Fattovich et al., 1997, Gastroenterology 112:463-472). It is estimated that the need for hepatic transplantation for infected individuals will increase 5-7 fold in the next 20 years unless more effective treatments and preventative programs are introduced (Davis et al., 1998, Hepatology 28 (Suppl 4, pt 2):99A).
While additional anti-viral therapies are needed to combat the spread of HCV, equally necessary is the development of a rapid, highly sensitive and cost-effective test to detect and monitor HCV within the population. Current PCR and ELISA-based assays for the detection of HCV are costly, relatively slow and reliant upon serum or plasma as the sample fluid. The substitution of oral fluid for serum in HCV assays would provide a cost-effective, non-invasive means to conduct routine screening and would facilitate sample procurement from patient groups where serum collection is difficult, such as intravenous drug users, who constitute a significant portion of total HCV cases.
A number of oral fluid-based assays have been designed for the detection of viral antibodies with good results. Virus-specific antibodies have been detected in the oral fluid of patients infected with human immunodeficiency virus (Major et al., 1991, J. Infect. Dis. 163:699-702), hepatitis A (Stuart et al., 1992, Epdiem. Infect. 109:161-166), hepatitis B (Ben Aryeh et al., 1985, Arch. Oral Biol. 30:97-99), rubella (Saleh, 1991, J. Egypt Public Health Assoc. 66:123-124) and following immunization against polio (Zaman et al., 1991, Acta Paediatrica Scan. 80: 1166-1173), rotavirus (Ward et al., 1992, J. Med. Virol. 36: 222-225) and hepatitis A (Laufer et al., 1995, Clin. Infect. Dis. 20:868-871). For HCV, ELISA-based assays developed initially for use with serum or plasma have been modified to detect anti-HCV antibodies in oral fluid (Cameron et al., 1999, J. Viral Hepatitis 6:141-144; Elsana et al., 1998, J. Med. Virol 55:24-27; McIntyre et al., 1996, Eur. J. Clin. Microbiol. Infect. Dis. 15:882-884; Sherman et al., 1994, Amer. J. Gastroent 89:2025-2027; Thieme et al., 1992, J. Clin. Microbiol. 30:1076-1079); using a modified protocol with the HCV 3.0 ELISA (Ortho Diagnostic Systems), (McIntyre et al. 1996, Eur. J. Clin. Microbiol. Infect. Dis. 15:882-884) detected anti-HCV antibodies within a group of 18 HCV(+) and 49 HCV(−) oral fluid samples with 72% sensitivity and 98% specificity. In the same study, 100% sensitivity and 100% specificity was achieved using the Monolisa HCV assay (Sanofi Pasteur Diagnostics, France). It is unclear what the differences were that lead to the increased sensitivity of the Monolisa test, and thus care must be taken in the interpretation of results obtained from tests not designed specifically for use with oral fluid. None of these assays has achieved the sensitivity required for a rapid point of care test. None of these assays has disclosed the special role of oral fluid IgA in human oral fluid as a key determinant of sensitivity and specificity for HCV screening.
An intrinsic difficulty in designing oral fluid-based diagnostic assays, however, is detecting a sufficient proportion of the relatively low levels of antibody present in oral fluid to generate a meaningful diagnostic result. Indeed, it is estimated that overall antibody levels are 800-1000-fold lower in oral fluid than in serum (Parry et al., 1987, Lancet 2:72-75) making detection sensitivity of the utmost importance in oral fluid-based tests. While this problem is significant, an HCV assay designed to be used specifically with oral fluid as the diagnostic fluid, and not simply a serum-based assay modified for use with saliva, could overcome this complication and provide an important test for HCV in the population.